The invention relates to power semiconductor components, in particular for high reverse voltages. The power semiconductor components include an n-doped silicon layer, into which a plurality of n- or p-doped layers are introduced between a first main area and a second main area. A cathode is assigned to the first main area and is formed by a first metallization layer. An anode, which is formed by a second metallization layer, covers the second main area.
Such power semiconductor components can be constructed in such a way that the layers, as seen from the second main area, include a p-doped anode zone, an n-doped stop layer which has a higher dopant concentration than a silicon layer which adjoins the stop layer.
Such components are widely known as bipolar transistors, thyristors or as field effect-controllable bipolar power semiconductor components, such as insulated gate bipolar transistors and are presented in U.S. Pat. No. 5,668,385 for example.
In another embodiment, the above-mentioned power semiconductor components can have layers which, as seen from the second main area, include a p-doped anode zone and, adjoining the latter, the n-doped silicon layer, adjoining that a stop layer, which has a higher dopant concentration than the n-doped silicon layer, and adjoining the stop layer an n-doped cathode zone.
Such power semiconductor components are generally known as diodes, and may either be present as discrete actual components or be contained as parasitic diodes in other power semiconductor components such as e.g. in power MISFETs (Metal-Insulator-Semiconductor Field-Effect Transistors). In a power MISFET, as is known, a parasitic p+-nxe2x88x92-n+ diode is reverse-connected in parallel with the actual MISFET from the source to the drain. Such power semiconductor components are likewise presented in U.S. Pat. No. 5,668,385 for example.
Such stop layers have hitherto been fabricated predominantly by deep diffusions which, however, require very long diffusion times. Furthermore, the doping profile also cannot be freely chosen as is disclosed in Published European Patent Application EP 0 214 485 A1.
Moreover, it is also known to deposit such stop layers epitaxially on a heavily n-doped substrate. However, epitaxy is a very expensive method, in particular with regard to the layer thicknesses required in power semiconductor components, and, in addition, has the problem that undesired, excessively high defect densities are quite often produced.
It is accordingly an object of the invention to provide a power semiconductor component which overcomes the abovementioned disadvantages of the heretofore-known components of this general type and which has a stop layer that does not have to be deposited epitaxially and which can be fabricated without necessitating lengthy deep diffusions.
With the foregoing and other objects in view there is provided, in accordance with the invention, a power semiconductor component, in particular for high reverse voltages, including:
an n-doped silicon layer;
a first main area and a second main area;
a plurality of doped layers introduced into the n-doped silicon layer between the first main area and the second main area;
the doped layers, as seen from the second main area, including a p-doped anode zone and an n-doped stop layer adjoining the p-doped anode zone;
the n-doped silicon layer having a first dopant concentration, the n-doped stop layer having a second dopant concentration higher than the first dopant concentration, the n-doped stop layer adjoining and completely covering the n-doped silicon layer;
the n-doped stop layer being doped with at least one dopant having at least one donor level between a valence band edge of silicon and a conduction band edge of silicon and the at least one donor level being more than 200 meV away from the conduction band edge of silicon;
a cathode assigned to the first main area and formed by a first metallization layer; and
an anode formed by a second metallization layer covering the second main area.
With the objects of the invention in view there is also provided, a power semiconductor component, in particular for high reverse voltages, including:
an n-doped silicon layer;
a first main area and a second main area;
a plurality of doped layers introduced into the n-doped silicon layer between the first main area and the second main area;
the doped layers, as seen from the second main area, including an anode zone, the n-doped silicon layer adjoining the anode zone, a stop layer adjoining the n-doped silicon layer, and an n-doped cathode zone adjoining the stop layer;
the n-doped silicon layer having a first dopant concentration, the stop layer having a second dopant concentration higher than the first dopant concentration, the stop layer completely covering the n-doped silicon layer;
the stop layer being doped with at least one dopant having at least one donor level between a valence band edge of silicon and a conduction band edge of silicon and the at least one donor level being more than 200 meV away from the conduction band edge of silicon;
a cathode assigned to the first main area and formed by a first metallization layer; and
an anode formed by a second metallization layer covering the second main area.
With the objects of the invention in view there is also provided, a semiconductor component, including:
a MISFET having a source, a drain, and a parasitic diode;
the parasitic diode being reverse-connected in parallel from the source to the drain and the parasitic diode including:
an n-doped silicon layer;
a first main area and a second main area;
a plurality of doped layers introduced into the n-doped silicon layer between the first main area and the second main area;
the doped layers, as seen from the second main area, including an anode zone, the n-doped silicon layer adjoining the anode zone, and a stop layer adjoining the n-doped silicon layer;
the n-doped silicon layer having a first dopant concentration, the stop layer having a second dopant concentration higher than the first dopant concentration, the stop layer completely covering the n-doped silicon layer;
the stop layer being doped with at least one dopant having at least one donor level between a valence band edge of silicon and a conduction band edge of silicon and the at least one donor level being more than 200 meV away from the conduction band edge of silicon;
a cathode assigned to the first main area and formed by a first metallization layer; and
an anode formed by a second metallization layer covering the second main area.
According to another feature of the invention, the at least one dopant includes selenium and/or sulfur.
According to another feature of the invention, the n-doped stop layer has a depth of between 1 xcexcm and 50 xcexcm.
According to yet another feature of the invention, the p-doped anode zone is embodied as a transparent emitter with a given depth and a given dopant concentration selected such that at least 50% of a total current flowing through the transparent emitter is carried by electrons. The given depth of the transparent emitter is preferably between 0.5 xcexcm and 5 xcexcm.
According to another feature of the invention, a plurality of IGBT (Insulated Gate Bipolar Transistor) cells including p-doped base zones and n-doped source zones are introduced from the first main area. The cathode is electrically conductively connected to the p-doped base zones and the n-doped source zones. A gate electrode is provided above the first main area and between respective two of the IGBT cells. An insulator insulating the gate electrode is also provided.
According to another feature of the invention, a p-doped base introduced from the first main area is provided. A plurality of n-doped cathode zones is introduced into the p-doped base, and the n-doped cathode zones are electrically conductively connected to the cathode.
According to another feature of the invention, a plurality of MCT (MOS-controlled thyristor) structures each including a p-type base, an n-type emitter, a channel region and a p-type short region is introduced from the first main area; and an insulated gate electrode is disposed above the first main area and between respective two of the MCT structures.
The object of the invention is achieved by virtue of the fact that the stop layer is doped with at least one dopant which has at least one donor level which lies between the valence band edge and the conduction band edge of silicon and is more than 200 meV away from the conduction band edge of the silicon. Such dopants are, in particular, sulfur or selenium. Sulfur has two donor levels, namely at 260 meV and 480 meV, and selenium has two donor levels, namely at 310 meV and 590 meV, below the conduction band edge.
Compared with the technically widespread donors, phosphorus, arsenic and antimony, whose energy levels are less than 50 meV away from the conduction band edge, this means that in the customary operating temperature range of power semiconductor components composed of silicon, i.e. in a temperature interval of approximately xe2x88x9255xc2x0 C. to +175xc2x0 C., only a very small proportion of the donor atoms is in thermal equilibrium in the ionized state.
Accordingly, the stop layer in the power semiconductor components according to the invention is xe2x80x9cactivexe2x80x9d only in the reverse mode or blocking mode of the power semiconductor component but not, however, in the forward mode. In other words, the number of atoms, which are produced by the impurities in the stop layer and act as dopants, changes depending on the operating mode of the power semiconductor component. This is achieved by virtue of the fact that, through the doping atoms, donor levels are provided which lie within the band gap of the silicon far away from the conduction band edge and from the valence band edge.
A further advantage of the use of sulfur or selenium as dopant is that the diffusion constants of both elements in silicon are very high compared with the dopants according to the prior art. The diffusion coefficients are shown in the comparison in FIGS. 5 and 6, which show a diffusion coefficient D of impurities in silicon versus reciprocal temperature 1/T.
The stop layer preferably has a dopant concentration ND of between 5xc3x971014 cmxe2x88x923 and 5xc3x971015 cmxe2x88x923, the stop layer having a depth of between 15 xcexcm and 35 xcexcm in the case of power diodes and having a depth of between 10 xcexcm and 25 xcexcm in the case of IGBTs (Insulated Gate Bipolar Transistors) and other controllable power semiconductor components.
Furthermore, the power semiconductor components according to the invention have an anode structure which optimizes the stop layer according to the invention for the anode-side limiting of the electric field in combination with provisions for the maximum anode-side extraction of charge carriers during the turn-off operation.
This is achieved by an anode emitter which is embodied as a transparent emitter and whose depth and charge carrier concentration are preferably chosen such that at least 50% of a total current flowing through the emitter is carried by electrons. A transparent emitter is to be understood hereinafter as an anodal emitter layer which is configured in such a way that a significant proportion of the total current leaves the anode metallization layer of the power semiconductor component as an electron current. This electron current specified in percent of the total current is referred to as emitter transparency. The emitter transparency is set by the depth and edge concentration of the anode emitter. As a result, high tail currents are avoided in the controllable semiconductor components according to the invention. By varying the depth of the stop layer, its maximum dopant concentration and its doping gradient, on the one hand, and by setting the dopant concentration and depth of the transparent emitter, on the other hand, it is possible to set a broad spectrum of turn-off current profiles over time. In other words, from an abrupt current chopping with minimal switch-off losses (hard recovery) through to a soft decay of the current with only slightly higher turn-off losses (soft recovery), all desired and conceivable switch-off current profiles can be attained.
The combination of the transparent anode emitter with the stop layer thus has the effect, inter alia, that during the turnoff operation the space charge zone penetrates into the stop layer and shifts or pushes the charge through the transparent emitter from i.e. out of the power semiconductor component. As a consequence of this, the current falls to 0 in a very short time, without the slowly falling tail currents which are typical in conventional structures. As a result, the turn-off losses are drastically minimized.
In a power diode, the stop layer is provided on the cathode side rather than on the anode side. In the power diode, as is known, the current changes its direction during the transition from the forward mode to the reverse mode. This phenomenon is known as xe2x80x9creverse recoveryxe2x80x9d in the literature. As explained above, the cathodal stop layer in the power diode prevents abrupt chopping of the current at the end of the reverse recovery phase. In a power diode, too, the transparent anode emitter can advantageously be combined with the cathodal stop layer since the simultaneous use of these two provisions can effect the minimization of the power diode thickness, in other words the minimization of the weakly n-doped layer between anode and cathode, in conjunction with weak injection from the anode side. This is the most effective way of reducing the reverse current peak. The cathodal stop layer thus ensures that the decay of the power diode reverse current is a soft process (soft recovery).
If the emitter transparency is set very high, then the forward resistance generally becomes too high for practical applications. However, this disadvantage can be remedied in a simple way by the transparent anode emitter being interspersed with heavily p-doped islands. This special embodiment corresponds to a further, preferred embodiment and can be employed both in power diodes and in controllable power semiconductor components.
In IGBTs, the power semiconductor components have, from the cathodal main area, a multiplicity of IGBT cells including p-doped base zones and n-doped source zones embedded therein, the cathode being electrically conductively connected to the base zones and source zones. Above the cathodal main area, a gate electrode which is insulated trough the use of an insulator is then provided between two respective IGBT cells.
In thyristors, from the cathodal main area, a p-doped base zone and, in the latter, a plurality of n-doped cathode zones are introduced, the cathode zones being electrically conductively connected to the cathode.
In the IGBTs, the transparent anode emitter preferably has a depth of less than 1 xcexcm, whereas in power diodes the transparent anode emitter typically has a depth of between 0.5 xcexcm and 5 xcexcm.
It is again emphasized that the stop layers according to the invention can also be used in a targeted manner in parasitic diode structures, i.e. the invention also extends inter alia to unipolar power semiconductor components. It is generally known that power MOSFETs have a parasitic diode structure reverse-connected in parallel with the actual power MOSFET from the source to the drain. For its part, this parasitic power diode has a diffusion capacitance and/or a depletion-layer capacitance which must be taken into account during the development and dimensioning of power MOSFETs. Accordingly, here too the invention opens up new ways of dimensioning and developing unipolar power semiconductor components.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a power semiconductor component for high reverse voltages, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.